The present inventions relates generally to a load cell and more particularly to a load cell for determining the weight and position of an occupant of a vehicle seat.
Generally, it is often desirable to determine the weight and position of an occupant of a seat in a vehicle passenger compartment. For example, based upon the weight of the occupant and the position of the occupant on the seat, an active safety restraint system may determine whether or not to deploy or may determine the amount of force with which to deploy. Applicant has determined that one way of achieving this is by using a plurality of load cells mounted beneath the vehicle seat. However, to get an accurate determination of weight and position, lateral and angular forces on the vehicle seat should be decoupled from the measurement.
One known type of load cell is disclosed in U.S. Pat. No. 6,005,199. It includes a load shaft having a half-spherical surface at each axial end. The load shaft is disposed between an upper pressure plate and a lower pressure plate. The half-spherical surfaces permit angular displacement between the upper pressure plate and the lower pressure plate. However, this design does not provide full lateral decoupling of the upper pressure plate. Further, this design is subject to interference from friction between interacting parts that contact each other in extreme positions. The friction causes mechanical hysteresis when measuring that may result in error.